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<h4 class="subsection">5.1.10 BOZ literal constants</h4>
<a name="index-BOZ-literal-constants"></a>

<p>Besides decimal constants, Fortran also supports binary (<code>b</code>),
octal (<code>o</code>) and hexadecimal (<code>z</code>) integer constants.  The
syntax is: &lsquo;<samp>prefix quote digits quote</samp>&rsquo;, where the prefix is
either <code>b</code>, <code>o</code> or <code>z</code>, quote is either <code>'</code> or
<code>&quot;</code> and the digits are <code>0</code> or <code>1</code> for binary,
between <code>0</code> and <code>7</code> for octal, and between <code>0</code> and
<code>F</code> for hexadecimal.  (Example: <code>b'01011101'</code>.)
</p>
<p>Up to Fortran 95, BOZ literal constants were only allowed to initialize
integer variables in DATA statements.  Since Fortran 2003 BOZ literal
constants are also allowed as actual arguments to the <code>REAL</code>,
<code>DBLE</code>, <code>INT</code> and <code>CMPLX</code> intrinsic functions.
The BOZ literal constant is simply a string of bits, which is padded
or truncated as needed, during conversion to a numeric type.  The 
Fortran standard states that the treatment of the sign bit is processor
dependent.  Gfortran interprets the sign bit as a user would expect.
</p>
<p>As a deprecated extension, GNU Fortran allows hexadecimal BOZ literal
constants to be specified using the <code>X</code> prefix.  That the BOZ literal
constant can also be specified by adding a suffix to the string, for
example, <code>Z'ABC'</code> and <code>'ABC'X</code> are equivalent.  Additionally,
as extension, BOZ literals are permitted in some contexts outside of
<code>DATA</code> and the intrinsic functions listed in the Fortran standard.
Use <samp>-fallow-invalid-boz</samp> to enable the extension.
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